Ball-point pen

ABSTRACT

A ball-point pen having a point assembly, in which the inside and outside diameters of a press formed portion (3) for preventing a ball (1) from slipping out, a sealing face (8), the projected amount of the ball, the diameter of a ball seat (16), the longitudinal backlash and the like are formed in optimized dimensions, sealing face (8) is configured so as to have a radius of curvature approximately equal to that of ball (1), and ball seat (16) having a radius of curvature approximately equal to that of ball (1) is formed in the rear of ball (1), while a multiple number of channels (4) for leading ink (13) to the pen point are provided inside the point assembly.

TECHNICAL FIELD

The present invention relates to parts of a point assembly in which aball disposed at its tip as a writing element is loosely held whilstbeing kept from slipping out with appropriately sized clearances whichestablish a flow passage of ink, and the invention further relates toimprovement of a ball-point pen using the parts.

BACKGROUND ART

Conventionally, there have been ball-point pens and small-tube typewriting implements where a cap with a sealing element therein composedof elastic rubber, etc., to seal the pen point is used when the pen isnot used for long periods of time, in order to prevent evaporation ofink and in order to prevent ink starvation which would occur due todrawing of air through the pen point when the pen is impacted by beingdropped as well as so-called forward leakage, that is, ink drip from thepen point. However, in the case of a clicking type ball-point pen aswell as in the case where the user has forgotten to fit the cap, in thecase of a writing implement where a volatile type of ink is necessary,and in other cases, ink starvation and air drawing tend to occur, andthe writing implement itself sometimes tends to become disabled.Countermeasures against such cases, include: inhibiting ink evaporationas much as possible by creating the parts of a ball-point pen, usingmetal; increasing the viscosity of ink (up to about 5,000 cp to 10,000cp); increasing the content of non-volatile solvent; decreasing theout-flow of ink by narrowing the ink flow passage in the point assembly;and creating an internal pressure in the barrel interior equal to orhigher than the pressure of the surrounding air to cause the interiorink to flow out. In particular, these problems have not been resolvedfor so-called intermediate type ball-point pens which use ink of amedium viscosity and present intermediate properties between oily andaqueous ball-point pens. Although ball-point pens of this type have suchimperfections, they have been put onto the market because of othermerits. Some ball-point pens which are improved as to these problemshave been invented, but no products are yet found which are free fromthe problem of abrasion in the interior of the point assembly.

In conventional ball-point pens, problems of forward leakage, airdrawing and dry-up due to ink evaporation are mainly preventedmechanically, by substantially sealing ink or the interior of the barreland pressurizing it (with a gas, or by pressing the barrel side face).Alternatively, if no such measures are used, a cap or an elasticmaterial such as rubber etc., for ensuring airtightness are closelyfitted on the pen point so as to protect the pen point. Whenmanipulation with a barrel mechanism is used as a measure, the mechanismneeds a complicated structure, which causes frequent mechanicalaccidents and is high in cost, thus increasing the price of theball-point pen. Products in which the only means for prevention is thecap are not the essential solution because the cap is kept off duringactual usage, and they also have the problem of deficiency inmaintaining performance if the user does not frequently fit the cap.Further, when ink is manipulated as a countermeasure, a solution isobtained at the sacrifice of the writing performance, such as sluggishdrying of drawn lines after writing, uncomfortable writing sensation,increased flow of ink as the pen point becomes abraded by the poorlubrication of the ink as it is used more, and slipping out of the ballor non-writing in the worst case.

The present invention is primarily to provide an improved writingimplement of the so-called ball-point pen type wherein a ball projectedfrom its tip as the writing point is loosely held with play inside thepoint assembly of a popular type and is kept from slipping out. Theinvention is to provide an inexpensive, high performance writingimplement having a point assembly which is able to prevent the problemsof dry-up, air drawing, forward leakage, etc., as well as the problem ofblotting, i.e., staining of the paper due to adherence of ink to the penpoint during writing, without needing a special ink or high-qualitybarrel mechanism and without compromising the manufacturing performanceof the sealing portion in the point assembly having a sealing portionfor sealing the interior from the outside air, by the combination of thewriting ball and the interior sealing face having a curvatureapproximately equal to that of the writing ball.

DISCLOSURE OF INVENTION

The present invention has been devised to solve the above problems, andthe gist of the invention is as follows:

The first feature of the present invention resides in ball-point pencomprising:

ink reservoir tube which stores an ink therein;

point assembly which is disposed in the front of the ink reservoir tubeand holds a ball to be a writing point at the front end thereof by meansof a press formed portion at the front end of the holder so that theball is rotatably projected from the front part thereof and is preventedfrom slipping out; and aqueous ink, characterized by meeting all thefollowing requirements 1) to 3):

1) the writing ball diameter φA, the diameter φJ of the ink holeconstituting interior ink passage, the ball seat angle P and the ballseat diameter φK satisfy the following relations:

    100°<P <150°

    φA×0.40<φJ<φA×0.80

    φA×0.50<φK<φA×0.90

2) three or more channel grooves constituting an ink passage duringwriting, are provided in the rear, with respect to the axial direction,of the ball, the channel grooves being terminated partway notpenetrating rearward to the ink reservoir tube, and the circumscribedcircle diameter φQ of the channels, the finished diameter φS, withrespect to transversal direction, of the side wall for limiting theloosely held ball, the ball projected amount H when the ball is put inclose contact with the ball seat and the ball seat diameter φK satisfythe following relations:

    φA×0.95<φQ <φA×1.05

    φA×1.02<φS<φA×1.10

    H×2.3<φK

3) the loosely held ball can move in the axial direction with alongitudinal backlash M falling within the range:

    φA×0.01<M<φA×0.10.

Next, the second feature of the present invention resides in theball-point pen defined in the above first feature, wherein the pointassembly incorporates an elastic element such as a spring therein whichconstantly urges the ball forward in the axial direction with a weakforce equal to or lower than 80 g.

The third and fourth features of the present invention reside in theball-point pen defined in the above first or second feature, wherein theink reservoir tube directly holds an aqueous ink having a viscosityranging from 10 cp to 4000 cp at 23° C. and a greasy follower in contactwith the ink at the rear end thereof, and all the parts which directlycome in contact with the ink, such as the point assembly, ink reservoirtube etc., are formed of materials having a water absorptivity of 0.2%or below at room temperature.

Further, the fifth feature of the present invention resides in aball-point pen comprising:

ink reservoir tube which stores an ink therein; and

point assembly which is disposed in the front of the ink reservoir tubeand holds a ball to be a writing point at the front end thereof by meansof a press formed portion at the front end of the holder so that theball is rotatably projected from the front part thereof and is preventedfrom slipping out, characterized by meeting all the followingrequirements 1) to 3):

1) the angle B of the tapered press formed portion, the writing balldiameter φA, the outside diameter φF of the press formed portion, theinside diameter φG of the press formed portion and the projected amountH of the ball satisfy the following relations:

    60°<B<100°

    φA×0.90<φF<φA×1.10

    φA×0.90<φG<φA×0.98

    φA×0.20<H<φA×0.40

2) the inside diametric portion has a circumferential sealing facehaving a width I and a radius of curvature approximately equal to theradius of the writing ball, I falling in the following range:

    φA×0.01<I<φA×0.15

3) the loosely held ball can move in the axial direction with alongitudinal backlash M falling within the range:

    φA×0.01<M<φA×0.10.

Moreover, the sixth feature of the present invention resides in theball-point pen defined in the above fifth feature, wherein acircumferentially, discontinuous ball seat K having a radius ofcurvature approximately equal to the radius of the ball is provided inthe rear, with respect to the axial direction, of the ball, the diameterφK falling in the following range:

    φA×0.6<φK<φA×0.9.

Next, the seventh and eighth features of the present invention reside inthe ball-point pen defined in the above fifth or sixth feature, whereinthe point assembly incorporates an elastic element such as a springtherein which constantly urges the ball forward in the axial directionwith a weak force equal to or lower than 80 g; the spring or elasticelement has an end turn portion or a substantially straight portionwhich is equivalent to the end turn portion, at the rear end thereof forstable placement; three or more channel grooves constituting ink passageduring writing are formed in the rear, with respect to the axialdirection, of the ball, the channel grooves being terminated partway notpenetrating rearward to the ink reservoir tube.

Next, the ninth through twelfth features of the present invention residein the ball-point pen having any one of the above fifth through eighthfeatures, wherein tapered portions C, D and E are formed in the rear ofpress formed tapered portion B; the width I of the interior sealing faceand the press formed width L on the outer side satisfy all the followingrequirements 4) to 6):

4) B>C, D>C, D>E,

5) 60°<B<100°, E<60°,

6) L×0.1<I<L.

Finally, the thirteen through twentieth features of the presentinvention reside in the ball-point pen having any one of the above fifththrough twelfth features, wherein the ink reservoir tube directly holdsan aqueous ink having a viscosity ranging from 10 cp to 4000 cp at 23°C. and a greasy follower in contact with the ink at the rear endthereof, the reduction amount from the writing element due toevaporation at a temperature of 23° C. under a humidity of 60% fallswithin the range of 0.06 mg/day to 0.8 mg/day (on the average over 30days).

As has been described, the ball-point pen of the present inventionincludes: a ball as a writing element which is rotatably placed at thetip so that it is projected outward but is prevented from slipping; andan ink reservoir tube containing ink therein. The interior of the pointassembly is configured so that the ink can be fed directly to therotatable ball as the writing portion through the ink passage which isconstituted from a multiple number of channel grooves sized asappropriate with transversal backlash and longitudinal backlash whichallows the ball to move in the up and down directions, and the like.

The ball is held loosely so as to freely rotate and is enclosed by meansof press forming such as plastic deformation so as not to slip off.

In the present invention, the interior edge of the press formed portionis prevented from abrading by providing a stable ball seat portion andink conduit portion by optimizing the projected amount of the ball, theball seat diameter, the diameter of a channel circumscribing circle, thefinished diameter and the like as well as by forming the ball seat,which is the rear-side abutment of the ball, with respect to the axialdirection, so as to create longitudinal backlash and so as to have aradius of curvature approximately equal to that of the ball, therebypreventing the ball from rolling out from the seat during writing.

As a further effective configuration of the present invention, the pointassembly may incorporate an elastic element such as a spring therein (tobe referred to as spring, hereinbelow) which constantly urges the ballforward with a weak force equal to or lower than 80 g. Here, when theaforementioned channel grooves are terminated partway instead of beingformed running through, the action of the spring can be ensured.

In particular, for so called `intermediate type ball-point pens` whichuse an aqueous ink having a viscosity ranging from 10 cp to 4000 cp at23±5° C., if the pen is configured without cap, the water content willevaporate from the ink producing the problem of deterioration of inkafter a long period of storage. In the present invention, all the partsin contact with ink are made up of materials having a water absorptivityof 0.2% or below. The specific examples include polyolefines such as PP,PE, etc., polybutylene terephthalate, polyethylene terephthalate, vinylresin, denatured polyphenylene ether, or other resins and alloy resinsof these, metals and metal-plated or metal-coated resins. The effects ofthe present invention can be more enhanced by the combination of thesewith the above point assembly.

In the present invention, a reliable press formed portion can be formedby optimizing the projected amount of the ball and inside and outsidediameters of the press formed portion so as to prevent the ball fromslipping out. In this case, press forming is performed by relativelystrong crimping until the inside diameter portion of the press formedportion abuts the ball so as to form a sealing face therein. Thissealing face will form a circumference having a fixed width and a radiusof curvature equal to that of the ball.

Further, the ball seat is formed so as to create longitudinal backlashand have a radius of curvature equal to that of the ball for abutment ofthe rear-side of the ball.

As a further effective configuration of the present invention, an openV-shaped tapered portion is formed in the rear of the press formedtapered portion and in front of the acute-angled tapered portion foruser's improved view. The ball seat is formed so as to have a diameterfalling within the range of φA×0.6 to φA×0.9 where φA is the balldiameter, preferably within the range of 0.7A to 0.8A. The width I ofthe sealing face is formed smaller than the width L of the exteriorpress formed portion, specifically formed to be one-tenth of L orgreater, preferably, 0.5L to 0.9L.

Further, an elastic element such as a spring (to be referred to asspring, hereinbelow) which constantly urges the ball forward with a weakforce equal to or lower than 80 g (preferably not greater than 20 g) isprovided. Here, when the aforementioned channel grooves are terminatedpartway instead of being formed running through, the action of thespring can be ensured.

In particular, for so called `intermediate type ball-point pens` whichuse an aqueous ink having a viscosity ranging from 10 cp to 4000 cp at23+5° C., the present invention becomes more effective.

Now, the actions of the above means for solution will be described. Inthe field of ball-point pens, in order to prevent ink evaporation, airdrawing into the point assembly, or in order to prevent ink starvation,backward leakage and forward leakage due to impacts from being dropped,a sealing part, generally composed of rubber, for sealing the tip isprovided for the cap; or a high viscosity ink or a ink which is noteasily evaporated is used. However, this produces other new problemssuch as necessity of frequent capping, sluggish drying of drawn linesand the like. Further, for prevention of the ball seat from beingabraded, a lubricant is added to the ink or included in an increasedamount, or a surfactant is used to reduce abrasion. However, thosecountermeasures related to the ink would cause the ink to blot on thepaper, or would cause the problem of forward leakage of ink from the pentip due to reduction in surface tension of the ink. Alternatively, anincreased amount of additives can deteriorate the ink stability overtime.

The improvement of the present invention makes it possible to solve theproblems related to abrasion by appropriately sizing the ball seat witha radius of curvature equal to that of the writing ball, whilst securingsufficient dimensions of other parts relating to abrasion. Thereby, itis possible to prevent the ball from coming out or prevent writingdisability.

In general, the writing implement is used to write whilst being inclinedat an angle of about 60° with the paper plane. Therefore, the larger theball seat, the less the ball tends to roll out from the ball seat duringwriting and hence the less abraded is the inner front edge of the pressformed portion. However, when the ball seat is too large, the flowpassage between the channels and the ball for securing ink flow isnarrowed, causing unstable ink flow and/or choking the channels duringwriting to cause writing disability. The present invention is alsoeffective in solving these problems simultaneously.

Further, the provision of a spring which constantly urges the ballforwards, produces reliable sealing performance as well as securesreliable sealing when the ball-point pen is oriented upward. Inparticular, the present invention functions most effectively when it isapplied to an intermediate type ball-point pen using an ink having arelatively low viscosity. For the ball-point pens of an aqueous ink typewhich are usable with a cap-less configuration, the total performance ofthe point assembly, having the sealability, and the spring incombination can be found out by the ink reduction from the writingelement due to evaporation. Accordingly, the parts to be used thereinare preferably made up of materials having as low a moistureabsorptivity (=water desorptivity) as possible. From thesespecifications, it is possible to provide a ball-point pen having stablequality.

In accordance with the improvement of the present invention, pressforming is performed so that a sealing portion will be formed so as tohave an interior shape equi-formed to the writing ball. Thereby, theseal for shutting out the external air can be made perfect. Further,since the angle of press forming and the inside and outside diametersafter press forming are optimized, it is possible to produce a perfectsealing surface free from fluctuation. Further the ink flow can bestabilized by setting the sealing width smaller than the width L of theexterior press formed portion and equal to or greater than one-tenththereof while securing sufficient dimensions of parts relating toabrasion. Thereby, it is possible to prevent the ball from coming out orprevent writing disability.

In general, the writing implement is used to write whilst being inclinedat an angle of about 60° with the paper plane.

Therefore, the open V-shaped tapered portion located in the rear of thepress formed portion, provides the function of preventing scratchinessagainst the paper surface as well as providing the function of forming awall of regulated thickness during press forming and hence stabilizingthe ink flow amount.

Further, the provision of a spring, which has an end turn portion at itsrear end as appropriate and hence provides continuous stable urging ofthe ball, produces a reliable sealing performance as well as securesreliable sealing when the ball-point pen is oriented upward. Inparticular, the present invention functions most effectively when it isapplied to an intermediate type ball-point pen using an ink having arelatively low viscosity. The exterior tapered configuration of thepresent invention functions to prevent the so-called blotting problem inthat ink climbs up the pen tip during writing and the collecting inkdrops after a certain period of time staining the paper, by inhibitingthe climbing of ink. Further, by limiting the size of the ball seat, itis possible to prevent the occurrence of abnormal abrasion in the pressformed portion and/or ball seat due to rolling of the ball duringwriting. Finally, a ball-point pen having stable quality can be given byregulating the reduction due to evaporation from the writing element,which indicates the total performance of the ink and the point assemblyhaving a sealing face, in combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional and external half view showing thestructure of a point assembly at the front end of a ball-point pen inaccordance with the first embodiment of the present invention;

FIG. 2 is a vertical sectional view showing the structure of afront-most part of a ball-point pen in accordance with the firstembodiment of the present invention;

FIG. 3 is a vertical sectional view showing the overall configuration ofa ball-point pen in accordance with the first embodiment of the presentinvention; and

FIG. 4 is a vertical sectional view showing the structure of a frontpart of a ball-point pen in accordance with the second embodiment of thepresent invention.

THE BEST MODES FOR CARRYING OUT THE INVENTION

FIGS. 1 to 3 illustrate an example of a ball-point pen of the firstembodiment of the present invention, and description will be madereferring to the figures.

An ink reservoir tube stores an ink, a greasy follower at the rear of,and in contact with, the ink and a solid follower rod 15 having aspecific gravity approximately equal to that of the follower, with theink and follower having been degassed during manufacturing. The follower14 is effective in preventing backward leakage and inhibitingevaporation. The follower rod 15 is floating in the follower and henceproduces capillary force so as to enable the follower to readily followthe ink 13 as the ink is consumed during writing. The following rod alsoprevents the follower from being broken and leaking when the pen isimpacted by being dropped. A writing ball 1 is fitted at the tip of thepoint assembly 2 so as not to fall off by the combination of the frontside press formed portion and the ball seat 16 on the rear side. Theball 1 is loosely held so as to be rotatable with a longitudinalbacklash M, formed in the front-to-rear direction, of φA×0.01 to φA×0.10(φA=ball diameter), or more preferably with a backlash of 0.03φA to0.08φA.

The press formed portion 3 is formed with a press forming angle of 60°to 100° (preferably 70° to 90°) by, usually, plastic deformation ofmetal, or the combination of plastic deformation and machining. Theinterior face of the press formed portion 3 is formed with a sealingsurface B having a radius of curvature which is approximately equal tothat of the ball so that the ball 1 abuts the sealing surface B tothereby substantially shut out the interior of the ball-point pen fromthe outside air, forming a so-called sealed state.

If the inside diameter of the press formed portion is large, the ball 1might come out causing writing deficiency due to slight wear at thefront inner part during writing. As to the ball seat 16, if it is large,the ball 1 is placed stably thereon, whereas if the seat is small, theball tends to roll off due to friction between the ball's rotation andthe ball seat during writing and may abrade the front inner diametricrim of the press formed portion. Further, if the ink conduit diameter istoo small, the flow amount is too low due to the narrow ink flowpassage. If the area of the ball seat (determined by the ink conduitdiameter and the ball seat 16 diameter) is too large, the contact areawith the ball 1 becomes so large to disturb the ball's smooth rotation.On the other hand, if the area of abutment is too small, the portion forreceiving the writing pressure is small, so that the ball seat maybecome abraded very quickly causing inability of writing due to sinkingin of the ball even when ink yet remains. In conclusion, it was foundthat simple control of individual dimensions cannot meet multipleconditions, and these dimensions will affect each other, to produce thefinal performance. Specifically, the optimal relationship was found tobe that where the ink conduit diameter φJ is 0.4 to 0.8 times of theball diameter φA (preferably 0.45φA to 0.65φA) and the ball seatdiameter φK is 0.5 to 0.9 times of φA (preferably 0.6φA to 0.8φA).

In general, it may be considered that when a greater sealing surface 8is formed by enhanced press forming, the product will be improved.However, an excessively large sealing surface 8 narrows the interiorspace and produces a greater friction with the ball to thereby reducethe amount of ink flow and degrade the writing performance. It has beenfound that in order to define the extent of press forming and thewriting performance, it is important to limit the dimensions such asprojected amount H of the ball, inner press-forming diameter φG, outsidediameter φF, sealing face width I, press forming angle B, longitudinalbacklash M, etc., in a related manner so as to satisfy the relationsdefined as follows. It was also found that a synergistic effect whichcannot be produced by each acting independently can be obtained. Thespecifications in parentheses indicate the ranges which are morepreferable.

    60°<B<100° (70° to 90°)

    φA×0.90<φF<φA×1.10

(1.01φA to 1.08φA)

    φA×0.90<φG<φA×0.98

(0.92φA to 0.97φA)

    φA×0.20<H<φA×0.40

(0.27φA to 0.35φA)

    φA×0.01<I<φA×0.15

(0.03φA to 0.10φA)

    φA×0.01<M<φA×0.10

(0.03φA to 0.08φA)

Illustratively, in view of adjusting the scratchy feeling of the ball tothe paper surface during writing, it is believed to be preferable (lessscratchy) that the projected amount of the ball be set as large aspossible. Therefore, this amount has been, in most cases, set at a valueabove which the ball can no longer be held. The inside and outsidediameters of the press formed portion were determined consequently bythe projected amount of the ball (i.e., when the projected amount of theball is smaller, the inside and outside diameters will be smaller). Evenin the case where the projected amount of ball is relatively large, ifthe outside diameter is large, the scratchiness against the papersurface becomes large. On the other hand, some having a large insidediameter are liable to be abraded, at the internal front part, bywriting, so that the ball would slip out resulting in a writingdeficiency. Besides, the projected amount of the ball, the inside andoutside diameters and the angle of press forming greatly affect thedimension of the inside sealing face. Briefly, it was found thatadjustment of each of these dimensions alone cannot meet the requiredmultiple performances and the different factors affect each other toproduce the final performance.

The ball seat provided at the rear of the ball is adapted to have thesame radius of curvature so as to produce a beneficial ball abutmentduring writing. The ball seat diameter φK is set 0.6 to 0.9 times of theball diameter φA in order to eliminate the problem of the ball slippingout from the ball seat due to the rotation during writing and abradingthe front interior part and in order to secure the required longitudinalbacklash. Ink 13 can move from the ink reservoir tube 12 to the interiorof the point assembly-and the ink flow passage to the ball is secured bychannels 4, longitudinal and transversal backlashes of the ball 1. It ismore effective if a spring 9 which continuously and slightly urges theball 1 forward is provided inside the point assembly 2 by formingcrimped points at the rear end of the point assembly 2. This spring 9may have a straight portion in the front part thereof to directly urgethe ball 1, or may have other configurations such that a spring 9 isused with a separate piece (not shown) whose rear end is urged by thespring 9, or the rear end of the spring may be fixed so as not to comeout, by a stepped portion in the bore of the joint 10 instead of crimpedpoints. Further, the spring 9 may be formed of resin, rubber or be aleaf spring etc. Any of these may be effective and show no difference.Here, an end turn portion or a substantially straight portion which isequi-formed to the interior of the fixture side is provided at the rearend of the spring so as to prevent the spring from popping out, incorporation with crimped points and thereby press the ball stably andstraightforwardly.

Setting relation of the seat angle P is analogous to that of theabove-described seat diameter. That is, when the angle is acute, theball tends to be directed toward the center during writing, whereas thistendency is less with a large seat angle. On the other hand, as to theflow amount of ink and durability against abrasion, the gap between theball 1 and channels 4 is easily blocked even with a slight abrasion whenthe seat angle is acute, whereas this blockage does not occur with alarge seat angle. Specifically, the seat angle P is optimally set at100° to 150°. It was also found that the longitudinal backlash M shouldbe effectively sized between 0.01 to 0.10 times of the ball diameter(more preferably 0.03A to 0.08A) since the longitudinal backlash M alsohas a significant effect on the flow amount of ink.

In general, the point assembly has an acute-angled tapered portion E(7)at the rear of the front press formed portion in order to improve theuser's view of the pen point during writing. Further, tapered portionsC(5) and D(6) which form a substantially open V-shape are provided toachieve a further improved view. When a sealing face is formed, inkbecomes more difficult to flow than in a configuration which is pressformed in a normal manner, since the ink passage becomes narrower andlonger. However, since this open V-shaped tapered configuration makes itpossible to reduce excessive wall thickness of the press formed portion,this prevents deformation of the interior, specifically, the ink passagefrom becoming unnecessarily too long. Further, surplus ink collectsaround the outer peripheral portion at the pen point and drops after acertain period of time. However, this open V-shaped tapered portion istoo steep to allow the ink to climb up, thus making it possible toprevent ink blotting.

The ink 13 used in the first embodiment has a viscosity of 10 cp to4,000 cp at the temperature of 23° C.±5° C. under normal shearing force,and comprises: water as the base, other solvents such as glycerin,propylene glycol etc., in an amount of 5 to 50%, pigments and/or dyes ascoloring agent in an amount of 1 to 20%, and other various additives,such as dispersant, gelatinizer, preservative, surfactant, moisturizeretc. as appropriate. Now, considering the reduction due to evaporationas it relates to total performance of ball-point pens, the use of thepoint assembly of the present invention improves the sealing performanceat the tip portion of the pen, so as to suppress the evaporation ofwater from the pen. This feature enables an ink which is usually knownto dry easily to be used in a cap-less ball-point pen. Even when thesealing face inside the point assembly is rather small and hence only alow amount of evaporation leakage occurs, no practical problem willoccur if the evaporation of the ink itself is low. When an excessiveamount of ink evaporates, the ink will reduce in amount duringtransportation and during storage before the user gets the product sothat the product cannot ensure the nominal writing distance (life) orcannot maintain its performance due to ink degeneration. When littleamount of ink evaporates (when the ratio of the non-volatile solvent isincreased), solidification of the ink at the pen point cannot beexpected and the ink adhering at the pen point absorbs moisture causingthe problem of forward leakage, or the problem that the drawn lines onthe paper will not dry quickly. In conclusion, in order to maintain thetotal performance of a ball-point pen of the present invention, it isimportant to control the reduction in weight due to evaporation when thepen has been left without cap at a temperature of 23° C.±5° C. under ahumidity of 60%±15% so as to fall within the range of 0.06 mg/day to 0.8mg/day (preferably 0.1 to 0.5 mg/day) on the average over 30 days. Insome cases even when the above conditions are met, a point assembly ofthe present invention may not overcome the above problems if the partsof the ball-point pen, which come in direct contact with the ink aremoisture-absorbing or moisture-desorbing. That is, in order to avoidloss of moisture from the ink reservoir tube 12, joint 10, etc., it isof course important to assemble these parts tightly so as to preventleakage, but also it is important to use materials having a moistureabsorptivity of 0.2% or below as the assembly parts. Here, the inkreservoir tube 12, joint 10 and follower rod are made up ofpolypropylene resin having a moisture absorptivity of 0.01%, while thepoint assembly is made up of stainless steel having a moistureabsorptivity of 0% and the follower at the rear end uses a mineral oilbased material having a moisture absorptivity of 0.01% or below.

FIG. 4 illustrates the second embodiment of the present invention, andits difference from the first embodiment is that the point assembly 2 isdirectly fixed by press fitting to the ink reservoir tube 12 instead ofusing a joint. The effects of this invention are the same as those ofthe first embodiment.

Table 1 shows the summarized results as to the conventional examples,examples and comparative examples in which the dimensions are different.For the evaluation of the examples, the measurement conditions, usedparts and set values are as follows:

[Ink and barrel body]: UM-100 black, a product of MITSUBISHI PENCILKABUSHIKI KAISHA, evaluated without cap; aqueous ink viscosity: 100 cp;and the barrel used and other parts are those on the market.

[Description of labels]

A: writing ball diameter; B: press forming angle; C and D: Open V-shapedtapered angle; E: acute tapered angle; F: outer press forming diameter;G: inner press formed diameter; H: ball projected amount; I: sealingface width; K: ball seat diameter; L: press formed width; and M:longitudinal ball backlash (refer to FIG. 1, unit: mm)

CONVENTIONAL EXAMPLE 1

A=φ0.5; E=30°; B=70°; F=0.98A; I=0 (none); H=0.4A; G=0.95A; M=0.03A;K=0.7A; C and D: none.

CONVENTIONAL EXAMPLE 2

A spring (15g) was incorporated in conventional example 1.

CONVENTIONAL EXAMPLE 3

an ink having double the non-volatile solvent was used, other settingswere the same as conventional example 1.

EXAMPLE 1

I=0.2; L=0.02A; C=20°; D=60°; H=0.35A; F=1.08A; G=0.97A, other settingswere the same as conventional example 2.

EXAMPLE 2

I=0.9; L=0.14A; H=0.3A; F=0.92A; G=0.91A, other settings were the sameas example 1.

EXAMPLE 3

K=0.85A, other settings were the same as example 1.

COMPARATIVE EXAMPLE 1

B=60°, I=0.4A, other settings were the same as example 1.

COMPARATIVE EXAMPLE 2

F=1.15A; G=0.99A, other settings were the same as example 1.

COMPARATIVE EXAMPLE 3

H=0.15A; K=none, other settings were the same as example 1.

The evaluation as to writing feeling, forward leakage, abrasion, inkflow, ink starvation, was made with three levels: ∘ for good, Δ forusable, and × for unusable.

Writing feeling: evaluated by observing the friction with paper duringhand writing;

Forward leakage: evaluated by observing ink leakage with the pen tipdown;

Durability against abrasion: evaluated based on the JIS machine writingtest to the end of ink;

Ink flow: evaluated based on the flow amount of ink and the density ofdrawn lines in the JIS machine writing test; State of ink starvationwithout cap; ink starvation during hand writing evaluated after the penwas left without cap 30 days and in a 23° C. 60% RH environment.

Ink reduction due to evaporation: reduction after 30 days in a 23° C.60% RH environment, measured by daily average.

The judgement was determined based on whether the invention can be usedas a cap-less ball-point pen. The unit for ink reduction was mg/day. Forthe inks having an evaporation amount of 0.8 or more, deterioration ofthe physical properties over time were observed from the storage test,so that the tests for those were omitted.

                  TABLE 1                                                         ______________________________________                                        Write     Forward Abra-  Flow  Starva-                                                                             Reduc-                                                                              Judge-                             feeling   leakage sion   Amount                                                                              tion  tion  ment                               ______________________________________                                        Conv. ◯                                                                         X       X    ◯                                                                       X     0.6   NG                               Ex.   Much forward leakage and ball slipped out,                              1     starvation was found without cap.                                       Conv. ◯                                                                         Δ X    ◯                                                                       Δ                                                                             0.5   NG                               Ex.   Abraded ball slipped out                                                Conv. ◯                                                                         X       X    ◯                                                                       ◯                                                                       0.05  NG                               Ex.   Heavy forward leakage, abrasion, drawn lines                            3     were undryed.                                                           Exam- ◯                                                                         Δ Δ                                                                            ◯                                                                       ◯˜Δ                                                         0.3   OK                               ple.  Little forward leakage, some abrasion without                           1     usage problem                                                           Exam- ◯                                                                         ◯                                                                         Δ                                                                            Δ                                                                             ◯                                                                       0.2   OK                               ple.  Some abrasion, somewhat lower flow amount                               2     without usage problem                                                   Exam- ◯                                                                         ◯                                                                         ◯                                                                      ◯                                                                       ◯˜Δ                                                         0.3   OK                               ple.  No problem                                                              3                                                                             Comp. ◯                                                                         Δ Δ                                                                            X     ◯                                                                       0.2   NG                               Ex.   Low ink flow amount with thin drawn lines                               1                                                                             Comp. X       Δ X    Δ                                                                             Δ                                                                             0.5   NG                               Ex.   Large friction with paper, ball slipped out.                            2                                                                             Comp. X       Δ X    ◯                                                                       ◯˜Δ                                                         0.3   NG                               Ex.   Large friction with paper, the ball seat was                            3     heavily abraded.                                                        ______________________________________                                    

The application of the present invention makes it is possible to solvethe problems of an intermediate type ball-point pen of a clicking typeusing aqueous ink, which were unfeasible to solve in the prior art, aswell as the problems of a ball-point pen having a cap with no sealingmember therein, and the problems of an oily ball-point pen and of adirect liquid type ball-point pen. Naturally, combination of the presentinvention with a conventional cap type or clicking type barrel mechanismmakes it possible to provide a further beneficial, distinctiveball-point pen.

Industrial Applicability

In accordance with the present invention, since it is possible to createreliable sealing at the pen tip, the pen does not need a cap or onlyneeds a simple type of cap, without the necessity of high sealingability therein. Therefore, it becomes possible to stably providelow-cost writing implements which are ready to be assembled as well aswriting implements of a clicking type which were unfeasible in the priorart. Further, since reliable sealing can be created, it is possible tosolve the problems concerning forward leakage, air drawing, inkstarvation and ball slipping out in connection with durability againstabrasion even in a ball-point pen using an aqueous ink which easily getsdry, without using any special ink or any complicated mechanisms. Inparticular, it is possible to expect more improved effects, in aconfiguration in which a spring is incorporated inside the pointassembly so as to continuously press the writing ball forward in closecontact with the interior sealing face of the present invention as wellas in a configuration in which the dimensions of the parts and/orreduction amount due to evaporation are set within the ranges of thepresent invention. The present invention is effective in solving most ofthe defects in a so-called intermediate type ball-point pen using amedium viscosity ink, which had many drawbacks. It is also possible toexpect further improved effects when the point assembly of the inventionis combined with a configuration using an ink having thixotropy, whichpresents a varying viscosity dependent on shear force so that the inkpresents a rather high viscosity during storage and a lowered viscosityduring writing due to the shear force from the ball. Moreover, thepresent invention can show the same effects if it is applied toconventional oily type ball-point pens or, sliver type ball-point pens,direct liquid type aqueous ball-point pens using an ink storage part ofmany comb-like slits and other types. The present invention is moreeffective in providing a problem-free writing implement when it iscombined with an anti-backward leakage mechanism such as a checkingvalve ball 11, etc.

What is claimed is:
 1. A ball-point pen comprising:ink reservoir tubewhich stores an ink therein; point assembly which is disposed in thefront of the ink reservoir tube and holds a ball to be a writing pointat the front end thereof by means of a press formed portion at the frontend of the holder so that the ball is rotatably projected from the frontpart thereof and is prevented from slipping out; and aqueous ink,characterized by meeting all the following requirements 1) to 3): 1) thewriting ball diameter φA, the diameter φJ of the ink hole constitutinginterior ink passage, the ball seat angle P and the ball seat diameterφK satisfy the following relations:

    100°<P<150°

    φA×0.40<φJ<φA×0.80

    φA×0.50<φK<φA×0.90

2) three or more channel grooves constituting an ink passage duringwriting, are provided in the rear, with respect to the axial direction,of the ball, the channel grooves being terminated partway notpenetrating rearward to the ink reservoir tube, and the circumscribedcircle diameter φQ of the channels, the finished diameter φS, withrespect to transversal direction, of the side wall for limiting theloosely held ball, the ball projected amount H when the ball is put inclose contact with the ball seat and the ball seat diameter φK satisfythe following relations:

    φA×0.95<φQ<φA×1.05

    φA×1.02<φS<φA×1.10

    H×2.3<φK

3) the loosely held ball can move in the axial direction with alongitudinal backlash M falling within the range:

    φA×0.01<M<φA×0.10.


2. The ball-point pen according to claim 1, wherein the point assemblyincorporates an elastic element such as a spring therein whichconstantly urges the ball forward in the axial direction with a weakforce equal to or lower than 80 g.
 3. The ball-point pen according toclaim 2, wherein the ink reservoir tube directly holds an aqueous inkhaving a viscosity ranging from 10 cp to 4000 cp at 23° C., and a greasyfollower in contact with the ink at the rear end thereof, and all theparts which directly come in contact with the ink, such as the pointassembly, ink reservoir tube etc., are formed of materials having awater absorptivity of 0.2% or below at room temperature.
 4. Theball-point pen according to claim 1, wherein the ink reservoir tubedirectly holds an aqueous ink having a viscosity ranging from 10 cp to4000 cp at 23° C. and a greasy follower in contact with the ink at therear end thereof, and all the parts which directly come in contact withthe ink, such as the point assembly, ink reservoir tube etc., are formedof materials having a water absorptivity of 0.2% or below at roomtemperature.
 5. A ball-point pen comprising:ink reservoir tube whichstores an ink therein; and point assembly which is disposed in the frontof the ink reservoir tube and holds a ball to be a writing point at thefront end thereof by means of a press formed portion at the front end ofthe holder so that the ball is rotatably projected from the front partthereof and is prevented from slipping out, characterized by meeting allthe following requirements 1) to 3): 1) the angle B of the tapered pressformed portion, the writing ball diameter φA, the outside diameter F ofthe press formed portion, the inside diameter φG of the press formedportion and the projected amount H of the ball satisfy the followingrelations:

    60°<B<100°

    φA×0.90<φF<φA×1.10

    φA×0.90<φG<φA×0.98

    φA×0.20<H<φA×0.40

2) the inside diametric portion has a circumferential sealing facehaving a width I and a radius of curvature approximately equal to theradius of the writing ball, I falling in the following range:

    φA×0.01<I<φA×0.15

3) the loosely held ball can move in the axial direction with alongitudinal backlash M falling within the range:

    φA×0.01<M<φA×0.10.


6. The ball-point pen according to claim 5, wherein a circumferentially,discontinuous ball seat K having a radius of curvature approximatelyequal to the radius of the ball is provided in the rear, with respect tothe axial direction, of the ball, the diameter φK falling in thefollowing range:

    φA×0.6<φK<φA×0.9.


7. The ball-point pen according to claim 6, wherein the point assemblyincorporates an elastic element such as a spring therein whichconstantly urges the ball forward in the axial direction with a weakforce equal to or lower than 80 g; the spring or elastic element has anend turn portion or a substantially straight portion which is equivalentto the end turn portion, at the rear end thereof for stable placement;three or more channel grooves constituting ink passage during writingare formed in the rear, with respect to the axial direction, of theball, the channel grooves being terminated partway not penetratingrearward to the ink reservoir tube.
 8. The ball-point pen according toclaim 7, wherein tapered portions C, D and E are formed in the rear ofpress formed tapered portion B; the width I of the interior sealing faceand the press formed width L on the outer side satisfy all the followingrequirements 4) to 6):4) B>C, D>C, D>E, 5) 60°<B<100°, E<60°, 6)L×0.1<I<L.
 9. The ball-point pen according to claim 8, wherein the inkreservoir tube directly holds an aqueous ink having a viscosity rangingfrom 10 cp to 4000 cp at 23° C. and a greasy follower in contact withthe ink at the rear end thereof, the reduction amount from the writingelement due to evaporation at a temperature of 23° C. under a humidityof 60% falls within the range of 0.06 mg/day to 0.8 mg/day (on theaverage over 30 days).
 10. The ball-point pen according to claim 7,wherein the ink reservoir tube directly holds an aqueous ink having aviscosity ranging from 10 cp to 4000 cp at 23° C. and a greasy followerin contact with the ink at the rear end thereof, the reduction amountfrom the writing element due to evaporation at a temperature of 23° C.under a humidity of 60% falls within the range of 0.06 mg/day to 0.8mg/day (on the average over 30 days).
 11. The ball-point pen accordingto claim 6, wherein tapered portions C, D and E are formed in the rearof press formed tapered portion B; the width I of the interior sealingface and the press formed width L on the outer side satisfy all thefollowing requirements 4) to 6):4) B>C, D>C, D>E, 5) 60°<B<100°, E<60°,6) L×0.1<I<L.
 12. The ball-point pen according to claim 1, wherein theink reservoir tube directly holds an aqueous ink having a viscosityranging from 10 cp to 4000 cp at 23° C. and a greasy follower in contactwith the ink at the rear end thereof, the reduction amount from thewriting element due to evaporation at a temperature of 23° C. under ahumidity of 60% falls within the range of 0.06 mg/day to 0.8 mg/day (onthe average over 30 days).
 13. The ball-point pen according to claim 6,wherein the ink reservoir tube directly holds an aqueous ink having aviscosity ranging from 10 cp to 4000 cp at 23° C. and a greasy followerin contact with the ink at the rear end thereof, the reduction amountfrom the writing element due to evaporation at a temperature of 23° C.under a humidity of 60% falls within the range of 0.06 mg/day to 0.8mg/day (on the average over 30 days).
 14. The ball-point pen accordingto claim 5, wherein the point assembly incorporates an elastic elementsuch as a spring therein which constantly urges the ball forward in theaxial direction with a weak force equal to or lower than 80 g; thespring or elastic element has an end turn portion or a substantiallystraight portion which is equivalent to the end turn portion, at therear end thereof for stable placement; three or more channel groovesconstituting ink passage during writing are formed in the rear, withrespect to the axial direction, of the ball, the channel grooves beingterminated partway not penetrating rearward to the ink reservoir tube.15. The ball-point pen according to claim 14, wherein tapered portionsC, D and E are formed in the rear of press formed tapered portion B; thewidth I of the interior sealing face and the press formed width L on theouter side satisfy all the following requirements 4) to 6):4) B>C, D>C,D>E, 5) 60°<B<100°, E<60°, 6) L×0.1<I<L.
 16. The ball-point penaccording to claim 15, wherein the ink reservoir tube directly holds anaqueous ink having a viscosity ranging from 10 cp to 4000 cp at 23° C.and a greasy follower in contact with the ink at the rear end thereof,the reduction amount from the writing element due to evaporation at atemperature of 23° C. under a humidity of 60% falls within the range of0.06 mg/day to 0.8 mg/day (on the average over 30 days).
 17. Theball-point pen according to claim 14, wherein the ink reservoir tubedirectly holds an aqueous ink having a viscosity ranging from 10 cp to4000 cp at 23° C. and a greasy follower in contact with the ink at therear end thereof, the reduction amount from the writing element due toevaporation at a temperature of 23° C. under a humidity of 60% fallswithin the range of 0.06 mg/day to 0.8 mg/day (on the average over 30days).
 18. The ball-point pen according to claim 5, wherein taperedportions C, D and E are formed in the rear of press formed taperedportion B; the width I of the interior sealing face and the press formedwidth L on the outer side satisfy all the following requirements 4) to6):4) B>C, D>C, D>E, 5) 60°<B<100°, E<60°, 6) L×0.1<I<L.
 19. Theball-point pen according to claim 18, wherein the ink reservoir tubedirectly holds an aqueous ink having a viscosity ranging from 10 cp to4000 cp at 23° C. and a greasy follower in contact with the ink at therear end thereof, the reduction amount from the writing element due toevaporation at a temperature of 23° C. under a humidity of 60% fallswithin the range of 0.06 mg/day to 0.8 mg/day (on the average over 30days).
 20. The ball-point pen according to claim 5, wherein the inkreservoir tube directly holds an aqueous ink having a viscosity rangingfrom 10 cp to 4000 cp at 23° C. and a greasy follower in contact withthe ink at the rear end thereof, the reduction amount from the writingelement due to evaporation at a temperature of 23° C. under a humidityof 60% falls within the range of 0.06 mg/day to 0.8 mg/day (on theaverage over 30 days).